Hydraulic pump with variable chamber



Dec. 9, 1969 Filed May 23; 1968 M. L. WOLF HYDRAULIC PUMP WITH VARIABLE CHAMBER 2 Sheets-Sheet 1 'INVENTOR. v MARVIN LWOLF M. L. woLF 3,482,521

HYDRAULIC PUMP WITH VARIABLECHAMBER Dec. 9, 1969 v 10?! 2 f- M n w z Q Q\ I 7 Filed May 23, 1968 United States Patent 3,482,521 HYDRAULIC PUMP WITH VARIABLE CHAMBER Marvin L. Wolf, Loveland, Ohio, assignor to The Cincinnati Milling Machine Co., Cincinnati, Ohio, a corporation of Ohio Filed May 23, 1968, Ser. No. 731,536 Int. Cl. F04b 49/00, 1/10, 1/00 US. Cl. 103-38 7 Claims ABSTRACT OF THE DISCLOSURE An axial pistoned, pintle ported, variable delivery hydraulic pump. Each pumping chamber has a springloaded control piston which moves when the pressure approaches the maximum pressure. Thus, when the pressure is at the maximum, the fluid shuttles back and forth in the chamber.

This invention belongs to the field of variable delivery hydraulic pumps. In the past, pumps of this type have varied delivery in one of two ways. In one type the effective displacement is changed by changing the angle of the swash plate which, in turn, changes the length of the stroke. In another type the timing is changed by nullifying part of the stroke by changing the position of the port with respect to the stroke.

The apparatus of this invention operates on the concept of an action of simultaneous reduction of the contracting action of the pumping chamber and of storing the volume of liquid until needed. As a result the system is eflicient since the high pressure shuttling oil does not require a large expenditure of energy. The system also has a fast speed of response since the chamber is always under pressure.

Referring now to the drawings:

FIG. 1 is a vertical section of the complete pump.

FIG. 2 is a section taken along line 22 of FIG. 1.

FIG. 3 is a partial section taken along line 33 of FIG. 1.

FIG. 4 is a partial section taken along line 44 of FIG. 1.

FIG. 5 is a partial section taken along line 5-5 of FIG. 1.

Referring now to the drawings, fluid enters the pump through inlet 1 and flows through passage 2 to the pintle 20. For convenience in manufacturing, the pintle 20 consists of a sleeve 20a and core 20b (FIG. 2). The fluid then flows through the pintle passage 3 into pintle inlet valve slot 4 (FIG. 5), and one of the individual cylinder inlet check areas 5 (FIG. 2). The fluid then proceeds past check valve 6 held in place by springs 7 and into the general pumping chamber 8. Chamber 8 alternately expands and contracts by the stroking action of the piston 23 being driven by the swash plate 22, which, in turn, is supported and driven by the pump drive shaft 21.

As the pumping chamber 8 contracts, the check valve 6 seats, and the fluid is forced out passage 24 to pintle exit valve slot 25. The fluid then flows through passage 26, to pintle slot 27, into area 28, and through the outlet 29. This is the way the pump operates when the outlet pressure is below the desired output pressure. This operation is no different than the operation of a standard fixed displacement pump.

During the conventional pumping phase, the wall of chamber 8 formed by piston 9 is stationary. This is insured by the bias spring 10- holding the piston 9 against the retainer 30. The hydraulic forces are in a state of balance, since orifice 11 and one Way leaf valve 36 admits the pumping chamber pressure to the control chamber 12.

When the system pressure reaches the desired level as determined by the pilot spool end area 19 and the pilot spring 17, the forces generated by the system pressure acting on the pilot end area 19 forces the pilot spool 15 to compress the pilot spring 17. This allows the fluid in the control chamber 12 of each piston chamber 8 to escape. The fluid in the control chamber 12 passes to the annular groove 13, through passage 14, into passage 16, to the pilot spring chamber 31, and out the drain 33. As the fluid flows from the control chamber 12, additional fluid will enter through the orifice 11. This incoming fluid will lose some of its pressure energy in going through the orifice 11. Thus, the pressure in control chamber 12 will lower with respect to the pumping chamber 8. This causes an unbalanced force to move piston 9 such as to make the volume of the pumping chamber 8 a constant. Due to this action, the volume of fluid delivered to the outlet passage 24 ceases or reduces depending on the relative velocities of the control piston 9 and the pumping piston 23. Thus, the action of piston 9 is to store the unneeded pressured volume of fluid produced by the pumping piston 23. The pumping piston 23 is ported from the inlet 1 of the pump to the oultet 29 by the action of the pintle 20, which is driven by an input drive shaft 21. The location of the various valve slots of the pintle 20 insures proper inlet outlet porting sequence. The stored volume of fluid is prevented from backflowing into the inlet by the check valve 6 and the blank area 35 (FIG. 3) of the pintle 20', which is located opposite the outlet valve slot 25.

Thus, the trapped volume of high pressure fluid is retained and will shuttle back and forth with the pumping piston 23 until the system needs it. The stored volume is still in communication with the outlet port during the normal discharge portion of the pumping cycle.

Each control piston 9 has a leaf check valve 36 (in FIG. 1 this valve is shown once in the open and once in the closed position) over the orifice 11. This check valve serves to prevent pressure loss in the control chamber 12 when the pumping piston is in the inlet portion of its cycle.

When the system demand is less than the pump full output, the control action is similar. A circulation of fluid from the control piston chamber of the pumping pistons on the discharge cycle to the control piston chambers of the pumping pistons on the intake cycle prevents cavitation between the control pistons as they move with the pumping pistons. When the control piston is stopped by the retainer 30, the inlet check valve 6 will open as the pumping piston reduces the pressure in chamber 8, and any needed fluid to fill the pumping chamber 8 will be drawn in. Thus, the pump can furnish all or any portion of its displacement to meet the system demand.

What is claimed is:

1. In a pump having an inlet and an outlet, the combination comprising:

(a) a plurality of chambers,

(b) means selectively to connect said chambers with the inlet and the outlet,

(c) a plurality of operating pistons, each said piston in communication with one of said chambers,

(d) means to reciprocate said operating pistons, and

(e) a plurality of control pistons, each in communication with one of said chambers and each operable in response to the pressure in the communicating chamber to yield for the storage of pressure fluid.

2. A combination as claimed in claim 1 further comprising:

(a) a drive shaft,

(b) means interconnecting said drive shaft to each said operating pistons such that as said drive shaft rotates each said operating piston reciprocates, and

(c) a pintle connected to said shaft for rotation therewith, said pintle selectively operable to connect each said chamber to the inlet and the outlet.

3. A combination as claimed in claim 1 wherein each said operating piston moves in a direction substantially perpendicular to each said control piston.

4. In a pump having. an inlet and an outlet, the combination comprising:

(a) a plurality of chambers in said pump,

(b) first means selectively to connect said chambers with the inlet and the outlet,

(c) a plurality of operating pistons, each in communication with one of the chambers,

(d) second means to reciprocate said pistons successively,

(e) a pilot valve,

(f) a plurality of control pistons each having one side in communication with one of the chambers, and each having the other side in communication with said pilot valve, and

(g) a passage connecting the other side of all said control pistons with said pilot valve.

5. A combination as claimed in claim 4 wherein each said control piston moves in a direction substantially perpendicular to the movement of each said operating pistons.

6. A combination as claimed in claim 4. further comprising:

(a) a drive shaft,

(b) a swash plate interconnecting said drive shaft to each said operating piston such that as said drive shaft rotates each said-operating piston recip'rocates,

(c) a pintle connected to said shaft for rotation therewith, said pintle selectively operable to connect each said chamber to the inlet and the outlet.

7. A combination as claimed in claim 4 further comprising a one way valve contained in each of said control pistons to prevent fluid from flowing from the pilot valve to the chamber.

References Cited UNITED STATES PATENTS 2,129,828 9/1938 Dunn 103-38 XR 2,286,063 6/1942 Condon 103-38 3,350,881 11/1967 DAmato 103-38 XR LEONARD H. GERIN, Primary Examiner US. Cl. X.R. 103161, 171 

